SE1350875A1

SE1350875A1 - Composition for coating a surface, coating, sampling device for thermal analysis of solidifying metal co-production of sampling device

Info

Publication number: SE1350875A1
Application number: SE1350875A
Authority: SE
Inventors: Patrik Popelar; Tobias Björklind
Original assignee: Sintercast Ab
Priority date: 2013-07-12
Filing date: 2013-07-12
Publication date: 2015-01-13
Also published as: CN104277503A; JP2015017250A; BR102014016962A2; KR102176221B1; MX351540B; US20150013477A1; US9109135B2; JP5714751B2; EP2824087A3; IN2014DE01711A; EP2824087B1; EP2824087A2; BR102014016962B1; CN104277503B; KR20150008001A; SE537286C2; MX2014008259A

Abstract

5 24 ABSTRACT The composition for coating of a surface intended to be exposed to a metal melt isdisclosed. The com position essentially consists of:8-18 wt-% of a refractory component50-75 vvt-% of solvent, preferably water10-20 vvt-% of an inorganic binder0-10 vvt-%, preferably 2-10 wt-%, of an organic binder,0.3-7 wt-%, preferably 2-6 wt-%, more preferably, 3-5 wt-% of pyriteand optionally up to 10 wt-%, preferably up to 5 wt-%, of additional additiveor additives.The composition results in a coating on a surface, which coating is able to reduce the dissolved elemental magnesium content in a metal melt to which the surface is exposed.

Description

A COMPOSITION FOR COATING OF A SURFACE, AND A COATING Field of lnvention The present invention relates to a composition for coating of a surface intended to beexposed to a metal melt, such as a surface of components used in the production of metalmelts, particularly in the production of cast iron, compacted graphite iron or ductile iron.The present invention also relates to a coating obtainable by means of coating a substratewith the composition. Furthermore, the present invention relates to a sampling device forthermal analysis of solidifying metal melts and a process for manufacturing such a sampling device.

Background Coatings may be used for example for providing a protective coating for a base metal,usually a ferrous metal, of ladles used for molten metal melts, such as aluminium,magnesium or zinc based melts. ln order to be effective, the coating must be fairly abrasionresistant, be sufficiently thick and adequately adherent to the surface of the base metal. ltis also possible to use coatings for achieving other functional purposes, such as when using reactive coatings.

Thermal analysis is a technique monitoring variations in temperature change of certainmolten substances during solidification to be able to determine the microstructure andhence properties of the substances in solid form. This is accomplished by taking a samplefrom the melt, transferring it into a sample vessel and recording and evaluating a time-dependent temperature change in the sample during solidification, by means of temperature responsive means, such as thermocouples or other devices known in the art.

WO 86/01755 discloses a method for producing compacted graphite cast iron by usingthermal analysis. A sample is taken from a bath of molten cast iron and this sample ispermitted to solidify during 0.5 to 10 minutes. The temperature is recorded simultaneouslyby two temperature responsive means, one of which is arranged in the centre of thesample and the other in the immediate vicinity of the vessel wall. So-called cooling curvesrepresenting the temperature of the iron sample as a function of time are recorded for each of the two temperature responsive means. According to this document it is then possible to determine the necessary amount of structure-modifying agents that must be added to the melt in order to obtain the desired microstructure.

Moreover, WO 92/06809 discloses a method for production of compacted graphite ironusing thermal analysis. A melt of a suitable composition and structure is prepared and amodifying agent, such as magnesium, is added to the melt in an amount which is expectedto be sufficient to produce compacted graphite iron. A sample is then extracted from themelt in a sample vessel, the wall of which is coated on its inside surface with a layerconsisting of a material which will react with dissolved elementary magnesium present inthe vicinity of said wall. Two thermocouples, one placed in the centre of the melt and theother in the vicinity of the vessel wall, are used to record the temperatures as a function oftime during solidification of the sample melt, thereby giving information of phasetransformations during solidification. The recorded temperature curves are thus used todetermine if the magnesium content and the inoculation of the melt, from which the samplehas been taken, has to be modified in order to achieve the desired phase transformationsof the melt when producing a casting thereof in order to achieve the desired structure ofgraphite in the casting.

The fact that the vessel wall is coated with a layer consisting of a material which will reactwith dissolved elementary magnesium, and the arrangement of the thermocouples in thesample, gives two separate temperature readings giving information regarding themagnesium content of the melt. The thermocouple in the vicinity of the vessel wall recordsa temperature curve of a melt with a predetermined lower level of dissolved elementarymagnesium (determined by the selected coating) than the thermocouple arranged in thecentre of the sample melt and thus the structural changes of said composition. Thus, bycomparing the readings of the two thermocouples, a more accurate measurement of themagnesium content of sample melt and thus the solidification properties of the melt fromwhich the sample has been taken, is achieved.

The use of a coating which reduces the content of magnesium in the vicinity of the vesselwall of a sampling device may also advantageously be used when conducting thermalanalysis of other metal melts, such as ductile cast iron (comprising nodulargraphiteparticles) or grey iron (comprising flake/lamellar graphite particles).

WO 97/35184 discloses a sampling vessel where a part of the inner surface is coated witha reactive layer, the layer being of a substance which will lower the concentration of dissolved elementary magnesium to increase the accuracy of the solidification structure predictions of molten cast iron. According to this document, one temperature responsivemeans is placed in the centre of the sample vessel, another temperature responsive meansis placed close to the inner surface of the sample vessel which has been coated with thereactive layer and a third temperature responsive means close to the inner surface of thesample vessel which has not been coated with the reactive layer. Each of the temperatureresponsive means are used to record the temperature of the melt during the solidificationprocess as a function of time to obtain temperatures which are to be evaluated todetermine the evolution of the solidification process. The reactive coating comprises 0-5 %sulphur, 0-10% oxides of silicon, manganese or iron and/or 0-0.5% oxides of potassium and sodium. lt has now been found that the previously known coatings for sampling devices intended tobe used for thermal analysis does not always work as intended and may be difficult to givesufficiently accurate readings during thermal analysis, especially in the case of thermalanalysis of ductile iron. Thus, there is still room for further improvements of previously known coatings.

Summary The object of the invention is a composition for coating of a surface intended to be exposedto a metal melt, which will result in a coating sufficiently adherent to the surface, sufficientlystable at high temperatures and which will enable a reduction of the elemental magnesium content of a metal melt in contact with the coated surface.

The object is achieved by a composition in accordance with independent claim 1, a coatingin accordance with independent claim 9 and a process for coating according to claim 18.Embodiments are defined by the dependent claims.

The present invention also relates to a sampling device for thermal analysis of solidifyingmelt in accordance with claim 19 and a process for manufacturing a sampling device for thermal analysis of solidifying melt in accordance with claim 20.

The composition for coating of a surface intended to be exposed to a metal melt essentiallyconsists of:8-18 wt-% of a refractory component50-75 wt-% of solvent, preferably water10-20 wt-% of an inorganic binder 0-10 wt-%, preferably 2-10 wt-%, of an organic binder,0.3-7 wt-%, preferably 2-6 wt-%, more preferably, 3-5 wt-% of pyriteand optionally up to 10 wt-% in total, preferably up to 5 wt-% in total, of one or more additional additives, and unavoidable impurities.

The refractory component is preferably selected from the group consisting of boron nitride,zirconia, alumina and mixtures thereof. Preferably, the refractory component is boron nitride.

The inorganic binder may suitably be a silicate, such as sodium silicate or potassiumsilicate. The organic binder may suitably be acrylic. The composition may also compriseone or more additional additives, such as additives selected from the group consisting ofsurfactants, viscosity modifiers, additives for flowability, additives for high temperature stability, additives for improved adhesiveness to a substrate, or mixtures thereof.

The pyrite is preferably in the form of a granular powder. Moreover, the average particlesize of the pyrite is preferably 40-70 um.

The composition as described above is used to coat a surface intended to contact a metalmelt. The coating may be performed by any suitable conventional coating technique knownin the art, such as brushing, painting or dipping of a substrate. The composition is thensubjected to a drying or evaporation step to essentially remove the solvent.

The com position adheres well to various types of substrates, such as metal surfaces andceramic surfaces, and is easy to apply thereto by conventional techniques. lt is also hightemperature resistant while still providing a sufficiently reactive coating. The fact thatsulphur is present in the form of pyrite ensures that it is sufficiently available for reactionwith dissolved elementary magnesium in the metal melt in contact with a coating obtainedby means of the composition.

The coating according to the invention, which is obtainable by means of the above givencomposition, essentially consists of: 26-60 wt-% of a refractory component 33-67 wt-% of an inorganic binder 0-3.5 wt-%, preferably 1.5-3.5 vvt-%, of an organic binder, 1-23 wt-%, preferably 6.5-20 wt-%, more preferably 10-16.5 vvt-%, of pyrite optionally up to 10 wt-°/», preferably up to 5 wt-%, of residual solvent, and optionally up to 33 wt-% in total, preferably up to 16 vvt-% in total, of one or more additional additives, and unavoidable impurities.

The sampling device for thermal analysis of solidifying metal according to the inventioncomprises a container adapted to comprise a sample quantity of a metal melt duringthermal analysis and temperature responsive means adapted to extend into the samplequantity during thermal analysis. The container comprises an inner surface adapted to facea sample quantity of the melt during thermal analysis, and an outer surface adapted to facethe ambient atmosphere during thermal analysis. At least a part of the inner surface,preferably the whole inner surface, of the container comprises the coating according to the invention. The container is preferably a doubled-wall container.

Examples of designs of the sampling device may for example be sampling devices asdisclosed in EP 1 034 419, WO 96/23206 or WO 97/35184, hereby incorporated byreference. The composition may be applied to the inner surface of any of the containers disclosed in these documents.

The sampling device simulates a spherical solidification of the molten metal inside thecontainer, which is the most reliable and accurate solidification shape for thermal analysis.

According to one embodiment, the sampling device comprises a container adapted to beimmersed into a metal melt and filled with a sample quantity of said metal melt. Thecontainer comprises a top part open at the top end thereof, a bottom part adapted to be thefirst part of the container immersed into the melt when taking a sample quantity, and anessentially cylindrical part arranged between the top part and the bottom part. Thecontainer further comprises an inner wall member and an outer wall member. The innerwall member has an inner surface intended to contact a sample quantity of the metal meltduring thermal analysis, and an outer surface. The outer wall member has an inner surface,and an outer surface adapted to be exposed to the ambient air during thermal analysis.The inner wall member and the outer wall member are essentially coaxially arranged in thecylindrical part of the container and joined at the top part of the container, and the inner andouter wall members define a closed insulating space between the outer surface of the innerwall member and the inner surface of the outer wall member. The sampling device furthercomprises temperature responsive means adapted to extend into the sample quantity during thermal analysis.

The bottom part of the container is preferably essentially semi-spherical in order to providethe intended simulation of a spherical solidification. The bottom part may also comprise aflattened part arranged at the bottom end of the bottom part and essentially perpendicularto a central axis of the container. The distance between the outer surface of the inner wallmember and the inner surface of the outer wall member at the flattened part may suitablybe smaller than the distance between the outer surface of the inner wall member and theinner surface of the outer wall member in the cylindrical part of the container. This further improves the heat loss and simulated spherical solidification.

The process of manufacturing a sampling device according to the present inventioncomprises providing a sampling device comprising a container. A composition as describedabove is applied to at least a part of an inner surface of the container, said inner part of thesurface of the container intended to face a metal melt during thermal analysis. Thereafterthe solvent of the composition is dried off or evaporated off such that a dry coating is achieved.

Even though the composition according to the present invention is mainly developed foruse in a sampling device for thermal analysis of solidifying metal melts, such as compactedgraphite iron and ductile iron, it may also be used for coating of other articles used inconnection with the production of metal melts. For example, the composition may be usedfor coating of ladles, troughs, moulds or any other surface of an article, such as a metalarticle, adapted to face a metal melt, particularly an iron, aluminium or zinc based melt.

Furthermore, a coating which reduces the content of magnesium in a metal melt in contactwith the coating may also be used in other applications, for example in applications wherea microstructural modification is desired in the surface of casting. For example, it may beused for achieving a microstructure at a surface of a cast component different than amicrostructure in the centre of the cast component such as for achieving differentproperties at the surface than in the bulk of the component.

Brief description of the drawingsFigure 1a illustrates a LOM (Light Optical Microscope) photograph of a surface of acasting obtained in contact with a coating obtained by means of a composition free from addition of pyrite.

Figure 1b illustrates a LOM photograph of a surface of a casting obtained in contactwith a coating obtained by means of a composition comprising 0.6 wt-%pyrite.

Figure 1c illustrates a LOM photograph of a surface of a casting obtained in contactwith a coating obtained by means of a composition comprising 2 wt-% pyrite.

Figure 1d illustrates a LOM photograph of a surface of a casting obtained in contactwith a coating obtained by means of a composition comprising 4 wt-% pyrite.

Figure 1e illustrates a LOM photograph of a surface of a casting obtained in contact with a coating obtained by means of a composition comprising 8 vift-Wo pyrite. ln the photographs of Figures 1a-1e, the distance mark in the lower right corner of each photograph indicates a distance of 100 um.

Detailed description The invention will be described in more detail below with reference to exampleembodiments and the accompanying drawings. The invention is not limited to the exampleembodiments discussed but may be varied within the scope of the appended claims.

The composition may be applied to a surface of an article by any suitable method known inthe art, such as painting, dipping, air-spraying or roller-coating.

The composition according to the present invention is particularly suitable for coating ofsampling devices used for thermal analysis of solidifying melts, and is especially suitablefor coating of sampling devices for thermal analysis of compacted graphite iron and ductile iron.

The composition for coating of a surface intended to be exposed to a metal melt accordingto the present invention essentially consists of: 8-18 wt-% of a refractory component 50-75 vvt-% of solvent, preferably water 10-20 vvt-% of an inorganic binder 0-10 vvt-%, preferably 2-10 vvt-%, of an organic binder, 0.3-7 wt-% of pyrite and optionally up to 10 vvt-% in total, preferably up to 5 vvt-% in total, of one or more additional additives, and unavoidable impurities.

The pyrite of the composition constitutes the functional addition which will enable reactionwith magnesium in the interface between the coating and the metal melt. Pyrite is an ironsulphide, essentially with the formula FeSz. lt is common knowledge that commercial pyritemay comprise impurities and the use of such commercial pyrite may suitably be used in thepresent invention without departing from the scope thereof. The sulphur in the pyrite willreact with dissolved elementary magnesium in the melt thereby reducing the magnesiumcontent available for assisting in the growth of various forms of graphite in a ferrous melt inthe vicinity of the surface which has been coated with a coating obtained by means of said com position.

As disclosed in WO 92/06809, the absolute values of the content of dissolved elementalmagnesium may vary based on for example other constituents in the melt from which asample is taken. WO 92/06809 discloses however one speciﬁc example wherein up to0.008 % Mg resulted in flaky graphite, 0.008-0.016% Mg resulted in compacted graphite,0.016-0.30% Mg resulted in a mixture of compacted and nodulargraphite, 0.030-0.035°/°Mg resulted in 80-100 % nodular graphite, and more than 0.035% Mg resulted in nodulargraphite. lrrespective of the specific conditions in each specific case, the necessary amountof added Mg to an iron based melt in order to achieve the desired microstructure in acasting thereof can be determined by performing thermal analysis of the melt, analysing theresult, and adding more Mg to the iron based melt, if necessary, followed by repeatedthermal analysis of the iron based melt with the additionally added Mg. Thermal analysis ofan iron based melt can be performed as many times as necessary to ensure that thedesired microstructure is achieved during subsequent casting of the melt. lt has been found that the sulphur of the coating cannot be added to the composition in anymanner. For example, it is not possible to add the sulphur in the form of elemental sulphursince elemental sulphur will burn off when the coating comes into contact with a metal melt,for example during thermal analysis using a sampling device which has been coated withthe coating. lf the sulphur is burnt off, it will not be available for reaction with the metal meltin contact with the coating. Tests have shown that elemental sulphur in a coating does notresult in the desired reduction of elementary magnesium. Therefore, it is essential that thesulphur of the coating is added in the form of pyrite.

The composition comprises at least 0.3 vvt-% pyrite, which is necessary in order to get thedesired function of a coating obtained by the composition. According to a preferredembodiment, the composition comprises at least 2 vvt-% of pyrite to be appropriately active, preferably at least 3 wt-% of pyrite.

Moreover, the composition comprises at most 7 wt-% of pyrite. Higher contents of pyritemay in some cases cause porosity or other damages in a casting obtained in contact with asurface comprising a coating obtained by the composition. Furthermore, higher amounts ofpyrite than about 7 wt-% are not expected to give additional benefits in terms of wallreaction and are therefore not necessary. According to a preferred embodiment, the composition comprises up to 6 wt-% pyrite, more preferably up to 5 vvt-% pyrite.

The amount of pyrite may in any case be selected based on the metal melt to which asurface coated by said composition should be exposed to. By way of example, if thecomposition is adapted to be used for producing a coating on a surface which is intendedto be exposed to ductile iron, the pyrite content of the composition may suitably be 3-6 vvt-%; and if the composition is adapted to be used for producing a coating on a surface whichis intended to be exposed to compacted graphite iron melt, the pyrite content of the composition may suitably be 0.3-5 wt-%, preferably 0.3-2 wt-%.

The pyrite is preferably added in the form of a granular powder. The average particle sizeof such a powder may suitably be 40-70 um to ensure sufficient properties of the coating.The particle size inter a/ia ensures that the pyrite may be evenly distributed in the coating.lf the particle size is too small, there is a risk of spontaneous crystallisation in thecomposition. lf the particle size is loo large, the pyrite may settle in the composition beforethe coating process has begun or in some cases even during the coating process, thereby causing uneven distribution.

The composition intended for coating of a surface intended to be exposed to a metal meltfurther comprises a refractory component. The refractory component is not intended to takepart in the magnesium reduction reaction and is therefore selected thereafter. Therefractory component should be stable at high temperatures and when in contact with metalmelts, such as a ferrous melt. According to one preferred embodiment, the refractorycomponent is boron nitride. Boron nitride is advantageous because it does not react withMg and the high interfacial tension between boron nitride and ferrous melts leads toreduced intimacy of contact and reduced likelihood of adhesion. Other suitable alternativesto be used as refractory component are zirconia and alumina because they are stable atvery high temperatures and will not react with a metal melt in contact therewith. lt is alsopossible to use any combination of boron nitride, zirconia and/or alumina as a refractory component of the com position according to the invention.

The refractory component is present in the composition in an amount of at least 8 wt-%,preferably at least 10 vvt-%, in order to provide the desired properties of a coating obtainedby means of the composition, such as high temperature stability and protection the coatedsurface to a metal melt. The composition comprises up to 18 wt-% of the refractorycomponent, preferably up to 16 wt-%, more preferably up to 14 vvt-%. Too high contents ofthe refractory component could in some cases make the composition difficult to apply to asurface to be coated by techniques such as dip coating or painting. Furthermore, too highcontents of the refractory component may in some cases result in cracking of a coatingduring use as a result of considerable thermal expansion of the substrate due to the hightemperature, especially in the case of metallic substrates. Moreover, the ratio between therefractory component and the binder(s) regulates the final properties of the coatingobtained by the composition, such as the adhesion to the substrate, green toughness and strength.

The refractory component of the composition may suitably have an average particle size ofabout 2-20 um, preferably 2-15 um. Other particle sizes of the refractory component arehowever also plausible depending on the refractory component selected and the othercomponents of the composition in order to ensure the desired properties of thecomposition, such as viscosity, risk of sedimentation etc.

The composition further comprises 50-75 wt-% of a solvent, preferably 55-70 vvt-%, morepreferably 60-68 wt-%. The solvent content inter alla regulates the application properties ofthe composition, such as thickness, uniformity and porosity, when applying the compositionto a substrate to be coated. The solvent may for example be an alcohol or water. Water ispreferable from an environmental and handling aspect. However, in some cases, forexample when coating of sand moulds, an alcohol is preferable in order not to influence thesand negatively. Furthermore, an alcohol may be faster to dry off whereas water may insome cases require forced air drying at a slightly increased temperature, such as about 35-50 °C. lVloreover, the composition comprises an inorganic binder which is compatible with therefractory component. The inorganic binder is present in an amount of 10-20 vvt-%,preferably 12-18 wt-%, of the composition and acts as a refractory binder. According to apreferred embodiment, the inorganic binder is a silicate in order to provide good heatstability. A silicate is also preferably from the point of view of providing less risk of cracking of a coating obtained by the composition, in case of substantial thermal expansion of the 11 substrate during use, as it imparts a certain plasticity to such a coating. Preferably, potassium silicate or sodium silicate is used.

Furthermore, the composition may also comprise an organic binder in an amount of up to10 wt-%, preferably 2-10 vvt%, of the composition and is intended to burn off during use ofthe coating in contact with a melt due to the high temperature. The organic binder is preferably acrylic.

The composition may also comprise one or more additional additives up to 10 wt-% in total.

Such additives may for example be selected from the group consisting of surfactants,viscosity modifiers, additives for flowability, additives for high temperature stability andmixtures thereof. For example, graphite may suitably be added in an amount of up to 2 wt-% for improving flowability and high temperature stability of the coating, especially whenthe composition comprises boron nitride as a refractory component. Moreover, diethyleneglycol monobutyl ether may be added in an amount of up to 5 wt-%, preferably 2-4 wt-%,for further improving the adherence of the coating to a metallic surface, such as a steel surface, if desired.

According to one specific embodiment of the present invention, the composition for coatingof a surface intended to be exposed to a metal melt essentially consists of:8-18 vvt-%, preferably 10-16 wt-%, of boron nitride50-75 vvt-%, preferably 55-70 wt-%, of water10-20 vvt-%, preferably 12-18 wt-% of potassium silicate2-10 vift-Wo, preferably 4-8 vvt-%, of acrylic,0.3-7 wt-% of pyrite,optionally up to 5 wt-% of diethylene glycol monobutyl ether,optionally up to 2 wt-% of graphite, andunavoidable impurities.

When the composition for coating of a surface intended to be exposed to a metal melt hasbeen applied to a substrate, the solvent of the composition is essentially removed, forexample by drying or evaporation. Drying may for example be performed by using forcedair drying at a slightly elevated temperature, such as about 35-50 °C. An essentially drycoating on a substrate is thus obtained.

The coating according to the invention essentially consists of:26-60 wt-%, preferably 33-55 wt-%, of a refractory component 12 33-67 vvt-%, preferably 40-60 wt-%, of an inorganic binder 0-3.5 wt-%, preferably 1.5-3.5 wt-%, of an organic binder, 1-6.5 wt-% of pyrite optionally up to 10 wt-°/», preferably up to 5 wt-%, of residual solvent, and optionally up to 33 wt-% in total, preferably up to 16 vvt-% in total, of one or more additional additives, and unavoidable impurities.

The refractory component, inorganic binder, organic binder, solvent and additionaladditives of the coating, respectively, are the same as has been mentioned in respect ofthe composition above and will therefore not be explained further. Since the coating isobtained by drying or evaporating the solvent, the particle sizes mentioned above remainsthe same. Furthermore, there may be residual solvent up to 10 wt-% remaining in thecoating after the drying and/or evaporation of solvent. Such residual solvent may be bound to the other components of the coating and the coating is therefore essentially dry.

The coating comprises at least 1 wt-% of pyrite, preferably at least 6.5 wt-% pyrite, andmore preferably at least 10 vvt-% pyrite. Furthermore, the coating comprises at most 23 wt-% pyrite, preferably at most 20 wt-% pyrite, more preferably at most 16.5 vvt-% pyrite.

According to one specific embodiment of the present invention, the coating essentiallyconsists of:26-60 vvt-%, preferably 33-55 wt-%, of boron nitride33-67 vvt-%, preferably 40-60 wt-%, of potassium silicate1.5-3.5 vvt-% of acrylic,1-23 vvt-% of pyriteoptionally up to 10 wt-%, preferably up to 5 wt-%, of residual water,optionally up to 16.5 wt-% of diethylene glycol monobutyl ether,optionally up to 6.5 wt-% of graphite and unavoidable impurities.

As mentioned above in regard to the composition for coating of a surface intended to beexposed to a metal melt, the amount of pyrite may in any case be selected based on themetal melt to which the coating should be exposed. By way of example, if the coating isadapted to be exposed to a ductile iron melt, the pyrite content of the coating may suitablybe 10-20 wt-%; and if the coating is adapted to be exposed to a compacted graphite iron melt, the pyrite content of the coating may suitably be 1-17 wt-%, preferably 1-6.5 wt-%. 13 As previously mentioned, the composition is especially suitable for coating of sampling devices for thermal analysis of solidifying metal melts.

A sampling device for thermal analysis comprises a container which is intended to beimmersed into a melt such that a sample quantity of the melt is allowed to flow into andfilling the container. The container, comprising the sample quantity, is then taken out of themelt and thermal analysis is performed. During the thermal analysis, the sample quantity isallowed to solidify and the temperature variation over time is measured using thetemperature responsive means. The temperature responsive means is suitably positionedby means of a support member. The support member may advantageously be locatedabove the top end of the container, preferably concentrically with a central axis of the container.

The container generally comprises a top part open at the mouth, i.e. open at the top endthereof, a bottom part adapted to be the first part of the container immersed into the meltwhen taking a sample quantity of the melt, and an essentially cylindrical part arrangedbetween the top part and the bottom part of the container. Furthermore, the containergenerally comprises an inner wall member having an inner surface intended to face thesample quantity, and an outer surface opposite the inner surface. The container generallyfurther comprises an outer wall member having an inner surface and an outer surface,wherein the outer surface is adapted to be exposed to the ambient atmosphere duringthermal analysis.

The inner and outer wall members may be essentially coaxially arranged at least in theessentially cylindrical part of the container around the central axis of the container. Theinner and outer wall members are suitably arranged at a distance from each other except atthe top part of the container where they are joined, for example by welding or the like.Thereby, a closed space may be formed between the inner and outer wall members. Thus, such a container is a double-walled container.

The inner and outer wall may suitably each comprise a radially extending flange arrangedat the top part of the container, the radially extending flanges of the inner and outer wallbeing joined together. Thereby, the inner and outer wall members are joined at the top endof the container, i.e. at the mouth thereof. The radially extending flanges of the inner andouter wall members may extend form the respective inner surface of the wall membersoutwardly in a direction from the central axis of the container such that they will not disturb the filling of the container during sample taking. 14 The distance between the inner and outer wall members and thus the dimensions of theclosed space is an important parameter in regulating the heat loss due to thermal radiationand thermal conduction. By selecting and fully or partly filling the closed space with asuitable medium, and/or altering the dimensions of the space, it is possible to adapt theheat removal rate of the sampling device to the values required for thermal analysis. Theclosed space may for example be evacuated or filled with gas. lt is also plausible to fill theclosed space with insulating materials, for example sand or various ceramics, 'rf desired.However, when the closed space is evacuated or filled with gas, such as air, radiation willbe an important heat transfer mechanism. As the temperature of the solidifying samplequantity increases, radiation will be of increasing importance since the effect thereof increases with the fourth power of absolute temperature.

The bottom part of the container is preferably semi-spherical in shape. Thus, an anglebetween a plane perpendicular to the central axis of the container and intersecting thecentral axis at the very bottom end of the container, and an imaginary line extending fromthe intersection of said plane and the central axis to the outer surface of the outer wallmember at the point where the bottom part and the essentially cylindrical part of thecontainer meet, is about 45°.

Suitably, both the inner wall member and the outer wall member of the container are semi- spherical in the bottom part of the container.

According to one embodiment, the container may further comprise a flattened part in thebottom part thereof. The flattened part is suitably arranged essentially perpendicular to thecentral axis of the container and has an essentially circular form concentric with the centralaxis of the container. Thus, an angle between a plane perpendicular to the central axis ofthe container and intersecting the central axis at the very bottom end of the container, andan imaginary line extending from the intersection of said plane and the central axis to theouter surface of the outer wall member at the point where the bottom part and theessentially cylindrical part of the container meet, is at most about 45°.

Suitably, both the inner wall member and the outer wall member each comprise a flattened bottom portion.

Moreover, the distance between the inner and outer wall members at the flattened part may suitably be smaller than the distance between the inner and outer wall members in the cylindrical part of the container. A sampling device comprising such a flattened bottom and the advantages thereof has for example been disclosed in EP 1 034 419.

The temperature responsive means utilised for thermal analysis of the sample quantity mayfor example be one or more temperature responsive sensors extending into the samplequantity. Preferably, at least two temperature responsive sensors are used. The firsttemperature responsive sensor is preferably arranged at the close vicinity of the inner wallmember ofthe container, whereas the second temperature responsive sensor preferably isarranged essentially in the centre of the sample quantity, i.e. essentially in the centre of thecontainer of the sample device. For example, in order to simulate the natural fading ofmagnesium of an iron-based melt that occurs in both ladle and in castings, the innersurface of the inner wall member, i.e. the surface which is adapted to face and be exposedto the sample quantity during thermal analysis, may be coated with a composition aspreviously described, thus obtaining the coating also described above. Convection currentsgenerated in the container as a result of the design thereof rinse the sampled iron along theinner surface of the inner wall member of the container and cause a low-magnesium iron toaccumulate in the stagnant flow-separated region at the bottom of the container. Thus, thetemperature responsive means arranged in the centre evaluates the non-reacted iron, thusdetermining the start-of-casting behaviour, while the temperature responsive meansarranged close to the inner surface of the inner wall member predicts the end-of-castingsolidification behaviour.

The temperature responsive sensors are preferably arranged in one or more protectivetubes. According to one embodiment, two or more temperature responsive sensors arearranged in one protective tube, which in turn is arranged in the sample device along thecentral axis of the container and extending into the container such that it will be immersedin the sample quantity during thermal analysis. ln such a case, the temperature responsivesensors are arranged inside the protective tube at different locations essentially along thecentral axis of container. lt is however possible to arrange temperature responsivesensor(s) in other manners, for example in different protective tubes and at essentially thesame distance parallel to the central axis from the top of the container. Also in thisembodiment, a first temperature responsive sensor may suitably be arranged in the closevicinity of the inner surface of the inner wall member whereas a second temperatureresponsive sensor is arranged essentially in the centre of the sample quantity during thermal analysis. 16 According to one embodiment, the support member may suitably be attached by legs to thecontainer. The legs enable a sample quantity of a melt to easily flow between the legs intothe container when the container is immersed in the melt from which the sample quantityshall be taken, thereby enabling an easy, consistent and reliable process for filling thecontainer with a sample quantity. Moreover, the support member may preferably act as alid to reduce radiation heat-loss from the top of the sample quantity during thermal analysis.This further aids in the construction of the sample device to simulate a sphericalsolidification of the sample quantity during thermal analysis, because it balances slower heat loss from the bottom of the container due to the construction thereof.

The inner and outer wall members of the container of the sampling device may for example be made of steel or other suitable material known in the art. ln accordance with the present invention, at least a part of the inner surface of the innerwall member, i.e. the surface which is adapted to face and be exposed to the samplequantity during thermal analysis, is coated with a composition as previously described, thusobtaining the coating also described above.

According to one embodiment, essentially all of the surfaces of the container which may beexposed to a metal melt during taking of a sample for thermal analysis and/or duringthermal analysis are coated using the coating composition according to the presentinvention. Furthermore, other surfaces of the sampling device may also be coated with thecomposition according to the invention without departing from the scope of the invention.

Other examples of sampling devices which may suitably be coated with the compositionaccording to the present invention includes the sampling devices disclosed in WO97/35184 and WO 96/23206.

The com position may be used for coating substrates intended to be exposed to a metalmelt, such as substrates of sands, ceramics and metals, such as steels. Thus, thecomposition may also suitably be used for coating of surfaces of for example sand moulds,permanent moulds, ladles, or the like, which surfaces are intended come into contact with ametal melt. ln fact, the composition according to the present invention may be used forcoating any surface which is intended to be exposed to a metal melt, especially when acoating capable of enabling a reaction with sulphur of a solidifying melt in the vicinity of such a surface is desired. 17 Experimental test 1 Sample compositions for coating of surfaces intended to contact a metallic melt wereproduced by adding different amounts of pyrite to a standard mould coating compositionsold under the trade name Teno Zir 6512 by Foseco which comprises zirconia as therefractory component, silicate as the inorganic binder and alcohol as solvent. The amount of added pyrite for the different sample compositions is disclosed in Table 1.

The sample compositions were applied by brushing to a hand moulded sand mould indifferent cavities of the same mould and dried. An iron based melt comprising about 3.7 wt-% C, 2.2 wt-% Si, 0.3 wt-% Mn and 0.006 wt-% S was cast in the different cavities of themould. Thereafter, the microstructure at the surface of the castings was investigated byoptical microscopy. The resulting depth of the flake skin developed at the surface of thecasting for each sample is given in Table 1. A depth of a flake skin is considered to be an average depth where flakes of graphite are detectable.

Table 1.Sample Amount of added pyrite Depth of flake skin Figure[wt-%] [mm] 1.1 0 0.2 Fig. 1a1.2 0.60 1.3 Fig. 1b1.3 2 1.3 Fig. 1c1.4 4 1.8 Fig. 1d1.5 8 2.7 Fig. 1e As can be seen from the results, a considerably thicker flake skin is achieved for samplecompositions comprising a pyrite addition compared to a sample composition where nopyrite has been added (Sample 1.1). Thus, it is clear that an addition of 0.60 wt-% pyritehas an effect on the microstructural changes of the melt during solidification. This is causedby the reaction of sulphur present in the pyrite component of the coating with the Mg of the iron based melt cast in the cavities of the mould.

Figures 1a-1 e show LOM photographs of the surface microstructure of the castingsobtained. As shown, and emphasized by arrows, in Figure 1e, when a composition of the coating comprising 8 wt-% pyrite was used, large porosities were noted resulting from large 18 areas of shrinkage. These appeared even close to the surface of the casting. Thus, an addition of 8 wt-% of pyrite is clearly disadvantageous.

Even though the experimental test described above was performed in a sand mould,similar results will also be achieved when used on a metallic mould or any other type ofmetallic substrate surface, such as a sampling device of metallic material coated with the sample compositions given above.

Moreover, it should be noted that even though the experimental test described aboveutilised a composition which comprises alcohol as the solvent, similar results may beexpected also for compositions for coating comprising for example water as the solventsince the solvent of the composition is essentially vaporised before the coating obtained by the composition comes in contact with the metallic melt.

Experimental test 2 Sample compositions for coating of surfaces intended to contact a metallic melt wereproduced by adding 2.3 wt-% pyrite to a composition comprising about 12 wt-% of boronnitride as the refractory component, about 74 wt-% of water as a carrier, about 15 wt-%potassium silicate as an inorganic binder, about 5 wt-% of acrylic as an organic binder andabout 4 wt-% of additional additives.

Sampling devices, having a configuration as described in EP 1 034 419, were coated withthe sample compositions by dip coating followed by drying at about 40 “C using forced air.The coated sampling devices were then used for thermal analysis of ductile iron under fullscale production conditions of ductile iron.

A stepping test was conducted wherein a sample was taken when the Mg content of theductile iron melt was at an initial low content, and the Mg content was increased stepwisesix times to the intended final Mg content of the ductile iron melt. Thus, a total of sevendifferent samples were taken. The reason was to determine if the pyrite content of thecoating was sufficient to enable determining different contents of Mg.

During thermal analysis, two temperature responsive means were used to recordtemperature curves during solidification of the sample quantities, one temperatureresponsive means arranged in the centre of the sample quantities and one arranged in the close vicinity of the inner surface of the container of the sampling device, and the heat 19 released by the reaction was calculated and evaluated in a manner as disclosed forexample in US 6 571 856, hereby incorporated by reference.

The result showed that the thermal heat release for the different samples ranged fromabout 20 J/g for the first sample (lowest Mg content) to about -3.7 J/g for the last sample(highest Mg content).

The range of the measurable thermal heat release is approximately 0-100 J/g and asuitable composition for use for coating of a sampling device for thermal analysis in fullscale production of a metal melt should preferably be in the lower part of said range inorder to also allow higher values within said range caused by normal variations during full scale production of metal melts.

The experimental test was repeated on another day (the average Mg-content in thesampled ductile iron might thus have been other than in the case above), but with a samplecomposition where 4 wt-% pyrite was added. The thermal heat release in this case rangedfrom about 41 J/g to about 12 J/g.

From the test results given above, it is clear that a 4 wt-% pyrite addition is better than a2.3 wt-% addition since it allows for more variations in full scale production. Morespecifically, the higher concentration of pyrite allows for measurements of irons that areover-treated with Mg whereas the lower concentration of pyrite is better for measuring ironthat is well under-treated with Mg. As the normal practice is to over-treat an iron-based meltwith Mg, the higher concentration of pyrite gives yields better resolution during thermalanalysis for such a condition. However, both pyrite contents provided acceptable results.

Experimental test 3 Three sample compositions for coating of surfaces intended to contact a metallic melt wereproduced by adding different amounts of pyrite to a composition comprising about 12 wt-°/°of boron nitride as the refractory component, about 74 wt-°/o of water as a solvent, about 15wt-% potassium silicate as an inorganic binder, about 5 wt-% of acrylic as an organicbinder and about 4 vvt-% of additional additives. The amount of added pyrite for thedifferent sample compositions was 3 wt-%, 6 wt-% and 9 wt-%, respectively.

Sampling devices, having a configuration as described in EP 1 034 419, were coated with the sample compositions by dip coating followed by drying at about 40 °C using forced air.

The coated sampling devices were used for thermal analysis of ductile iron under full scaleproduction conditions of ductile iron. The experiment was performed in the same ductile iron melt for all three sample compositions.

Thermal analysis was used to determine the thermal heat release in the same way asdescribed in Experimental test 2. lt was found that the thermal heat release for the sample composition comprising 3 wt-%pyrite was about 42 J/g, whereas the thermal heat release for both the sample compositioncomprising 6 vvt-% pyrite and the sample composition comprising 9 wt-% pyrite were about58 J/g. Thus, it is clear that an increase of pyrite content from 3 wt-% to 6 wt-% increasesthe heat release and the results thus indicate an increase in the consumption of elementaryMg from the melt with increasing pyrite content, whereas increasing the pyrite content from6 wt-% to 9 wt-% have no substantial effect. Thus, the pyrite content can suitably be keptlower than 9 wt-% for optimisation of results obtainable during thermal analysis of iron melts with common Mg levels.

Claims

1. A composition for coating of a surface intended to be exposed to a metal melt, the composition essentially consisting of: 8-18 wt-% of a refractory component 50-75 vvt-% of solvent, preferably water 10-20 vvt-% of an inorganic binder 0-10 vvt-%, preferably 2-10 wt-%, of an organic binder, 0.3-7 wt-% of pyrite and optionally up to 10 wt-% in total, preferably up to 5 vvt-°/0 in total, of one or more additional additives, and unavoidable impurities. The composition according to claim 1, wherein the refractory component is selectedfrom the group consisting of boron nitride, zirconia, alumina and mixtures thereof, preferably boron nitride. The composition according to any of the preceding claims, wherein the inorganicbinder is a silicate, preferably a silicate selected from sodium silicate or potassiumsilicate. The composition according to any of the preceding claims, wherein the organicbinder is acrylic. The composition according to any of the preceding claims, wherein the one or moreadditional additives is/are selected from the group consisting of surfactants,viscosity modifiers, additives for flowability, additives for high temperature stability,additives for improved adhesiveness to a substrate. The composition according to any of the preceding claims, comprising 2-6 wt-% ofpyrite, preferably 3-5 vvt-% pyrite. The composition according to any of the preceding claims, wherein the pyrite is inthe form of a granular powder, preferably with an average particle size of 40-70 um. The composition according to any of the preceding claims, wherein the average particle size of the refractory component is 2-20 um. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 22 A coating essentially consisting of: 26-60 vvt-% of a refractory component 33-67 vvt-% of an inorganic binder 0-3.5 wt-%, preferably 1.5-3.5 wt-°/>, of an organic binder, 1-23 wt-% of pyrite optionally up to 10 wt-°/», preferably up to 5 wt-%, of residual solvent, and optionally up to 33 wt-% in total, preferably up to 16 vvt-% in total, of one or more additional additives, and unavoidable impurities. Coating according to claim 9, wherein the refractory component is selected from thegroup consisting of boron nitride, zirconia, alumina and mixtures thereof, preferably boron nitride. Coating according to claim 9 or 10, wherein the inorganic binder is a silicate, preferably a silicate selected from sodium silicate or potassium silicate.Coating according to any of claims 9-11, wherein the organic binder is acrylic. Coating according to any of claims 9-12, wherein the one or more additionaladditives is/are selected from the group consisting of surfactants, viscositymodifiers, additives for flowability, additives for high temperature stability and additives for improved adhesiveness to a substrate. Coating according to any of claims 9-13, comprising 6.5-20 wt-% of pyrite,preferably 10-16.5 vvt-% pyrite. Coating according to any of claims 9-14, wherein the average particle size of pyriteis 40-70 um. Coating according to any of claims 10-16, wherein the average particle size of the refractory is 2-20 um. An article comprising a substrate, such as a metallic substrate, and a coatingaccording to any of claims 9-16. Process for coating of an article, such as a metallic article, comprising applying thecomposition according to any of claims 1-8 to at least a part of the article followed by drying and/or evaporation of the solvent. 19. 20. 21 23 A sampling device for thermal analysis of solidifying metal, comprising a containeradapted to comprise a sample quantity of a metal melt during thermal analysis andtemperature responsive means adapted to extend into the sample quantity duringthermal analysis, the container comprising an inner surface adapted to face asample quantity of the melt during thermal analysis, and an outer surface adaptedto face the ambient atmosphere during thermal analysis, characterised in that atleast a part of the inner surface of the container comprises a coating according toany of claims 9-16. Process of manufacturing a sampling device for thermal analysis of solidifyingmetal, the process comprising providing a sampling device comprising a containeradapted to comprise a sample quantity of a metal melt during thermal analysis thecontainer comprising an inner surface adapted to face a sample quantity of the meltduring thermal analysis, and an outer surface adapted to face the ambientatmosphere during thermal analysis, characterised in applying a compositionaccording to any of claims 1-8 to at least a part of the inner surface of the containerand subjecting the composition to a drying and/or evaporation step. . Process according to claim 20, wherein applying said composition is performed by painting or brushing the inner surface of the container with the composition ordipping the container into said composition.